linux-kernel - Re: [PATCH v2 3/3] xfs: Add alignment check for DAX mount

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Date:	Mon, 2 May 2016 13:50:27 -0600
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	dan.j.williams@...el.com, jack@...e.cz, david@...morbit.com,
	hch@...radead.org, boaz@...xistor.com, tytso@....edu,
	adilger.kernel@...ger.ca, ross.zwisler@...ux.intel.com,
	micah.parrish@....com, linux-nvdimm@...ts.01.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] xfs: Add alignment check for DAX mount

On Mon, May 02, 2016 at 12:42:58PM -0600, Toshi Kani wrote:
> When a partition is not aligned by 4KB, mount -o dax succeeds,
> but any read/write access to the filesystem fails, except for
> metadata update.
> 
> Call bdev_direct_access to check the alignment when -o dax is
> specified.
> 
> Signed-off-by: Toshi Kani <toshi.kani@....com>
> Cc: Dave Chinner <david@...morbit.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Boaz Harrosh <boaz@...xistor.com>
> ---
>  fs/xfs/xfs_super.c |   23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 187e14b..b7ee323 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1557,15 +1557,30 @@ xfs_fs_fill_super(
>  		sb->s_flags |= MS_I_VERSION;
>  
>  	if (mp->m_flags & XFS_MOUNT_DAX) {
> +		struct blk_dax_ctl dax = {
> +			.sector = 0,
> +			.size = PAGE_SIZE,
> +		};
>  		xfs_warn(mp,
> -	"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
> +		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>  		if (sb->s_blocksize != PAGE_SIZE) {
>  			xfs_alert(mp,
>  		"Filesystem block size invalid for DAX Turning DAX off.");
>  			mp->m_flags &= ~XFS_MOUNT_DAX;
> -		} else if (!sb->s_bdev->bd_disk->fops->direct_access) {
> -			xfs_alert(mp,
> -		"Block device does not support DAX Turning DAX off.");
> +		} else if ((error = bdev_direct_access(sb->s_bdev, &dax)) < 0) {
> +			switch (error) {
> +			case -EOPNOTSUPP:
> +				xfs_alert(mp,
> +			"Block device does not support DAX Turning DAX off.");

Since you're already in here editing all the strings, can you add a period to
make it more readable?   Applies to all strings.

> +			"Block device does not support DAX. Turning DAX off.");
							  ^

> +				break;
> +			case -EINVAL:
> +				xfs_alert(mp,
> +			"Partition alignment invalid for DAX Turning DAX off.");
> +				break;
> +			default:
> +				xfs_alert(mp,
> +			"DAX access failed (%d) DAX Turning DAX off.", error);

I DAX think you might DAX have too many DAXes in here. :)

> +			}
>  			mp->m_flags &= ~XFS_MOUNT_DAX;
>  		}
>  	}

Other than the nit-picking about the strings, this seems fine.

You can add this for the series:
Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>